Due to the chibi nature of the game, this estimate must be considered as a rough corresponding real life height estimate of the character. The game is set in a middle ages fantasy premise, so therefore we assume that the Knight belongs to a proportion of male average height during the middle ages.
According to Richard Steckel, the average male height was around 173.4 centimeters during the early middle ages, this is something which later on started to drop to 167cm during the 17th and 18th century. This data was taken from one Ohio State News article.
If our assumption (that the knight is a Middle Ages European) is correct, then we can have a conclusion that the Knight is around 5 feet and 9 inches tall in height (173cm).
Another possible height that can be given to the Knight, especially since the world is set in a mythical theme, is that he can be around 3 feet tall. When observing the scale difference between the knight and some kobold in this Youtube Game Review, it appears that the Knight stands a few inches taller than the mythical creature “kobold”. Kobolds in general are a type of monster in many games and they are often portrayed to be goblin like in stature, meaning they measure only around 2 to 2.5 feet tall. If such is the case, then the Knight may just be around 3 feet tall.